I just listened to the brew strong episode from nov 29 2010. In it the hosts talk about not boiling LME but instead just adding it straight to the fermentor, or really late in the boil. I have been boiling mine for the full 60 min as instructed by my LHBS. Question is. -What is the point to not boiling the LME for the full time? -Can this be done with any LME? I think my LHBS buys in bulk and re-packages (it comes in a plastic tub with thier label but still says it is coopers) -How will this effect the beer overall in regards to color, clarity, taste etc? -In regard to these questions, does it change if I do a partial (2.5 gal) boil or a full boil?

2 Answers
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The point behind adding the LME late in the boil or straight to the fermenter is that the sugars in the LME will undergo the Maillard reaction during the boil. The gravity also affects the hop utilization rate. You need SOME sugars in the wort to isomerize the hop alpha acids, but the stronger the wort the less a given hop addition will bitter.

Recipes are designed to be boiled full-volume with all the extract/sugars in them. If you full-boil, adding the extract late will probably give you results that are a little lighter in color, and a bit more bitter than the style/recipe would lead you to believe.

If you partial-boil and throw all the LME in for all 60 minutes, more Maillard Reaction and less hop bittering will occur. Darker, sweeter beer.

Partial boil with SOME of the LME in for 60 minutes and the rest in for about 5-15 minutes (I've seen differing references): You will likely get something similar to a full-boil, full-extract brew.

Partial boil with ALL of the LME in the late stages of boil: It is my understanding that the hops won't extract until there are some sugars in the wort. Translation: No LME, no/significantly less hop extraction (but I've never verified this if anyone can set me straight, please comment and I'll edit) . Result: Lighter, sweeter beer.

Personally, I typically use 2 of the 3 pound (1.5 kilo) cans in most of my beers. I'll add while bringing up the temperature to boiling, and add the second one at about 15 minutes left on the boil, typically wherever there is a hop addition.

@Denny, I heard it explained as caramelization, but what SHOULD it be called when the sugars darken in color while boiling in solution? I agree that caramelization occurs once the temperature gets significantly above the boiling point, but have no better term.
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PulseheadFeb 23 '11 at 18:49

maltose caramelization happens at 365F, just as a reference for people. Actually the Malliard reactions happen at 320ish I think too. So pulseheads questions are good indeed. Lets bump this out to a new question and see what floats up.
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brewchezFeb 23 '11 at 19:34

If you are doing full boil then the main reason to add LME late is because of color. LME already tends to be darker than DME or all-grain wort. Boiling it for a long time just makes it darker.

If you are doing partial boil then adding LME late is going to change your hop utilization. The gravity of a partial boil is higher than a full boil, and hop utilization is lower in high-gravity wort. By moving some or all of your LME to late in the boil, you lower the gravity for most of the boil and increase your hop utilization.

I can't think of any reason why you couldn't do this with any LME. If you're using pre-hopped LME then your process will be different, though.

In the most recent Brew Strong - Hops & Water Revisited (thebrewingnetwork.com/shows/719), Palmer & Jamil sort of went back on the long-accepted notion that adding ME late will affect IBUs in the beer. They talked about recent tests that indicated that wort gravity doesn't impact hop utilization. Your point about color definitely still stands, though.
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JackSmithFeb 23 '11 at 14:25